(i) Field of the Invention
This invention relates to procedures for reducing the viscosity and density of heavy oils to make them more suitable for transportation by pipeline from the field to refineries for further processing. This invention also relates to processes for the generation of both hydrogen and carbon dioxide by one of two alternative schemes: either only reducing the viscosity and density of the heavy oils to a small extent by minimizing thermal cracking; or totally changing the properties of the heavy oil by operating at typical hydrocracking conditions.
(ii) Description of the Prior Art
The decreasing supply of light conventional crudes is spurring the use of more heavy oils and bitumen. Much of this heavy oil production is transported by pipeline from the field to refineries for further processing. For example, significant quantities of heavy oil are transported from western Canada to the United States where they are used in asphalt production. However, many of the heavy oils produced do not meet the specifications set by the pipeline companies for viscosity, density and bottoms, sediment and water (BS&W). Currently these oils are blended with large amounts of diluent (natural gas condensate or lighter petroleum fractions) to meet the specifications. However, demand and supply predictions for heavy oil and diluents indicate that a shortage in diluent will develop during the 1990's.
An increasing fraction of the heavy oils are being produced by enhanced oil recovery (EOR) techniques, e.g. steamflood, carbon dioxide flooding or fireflood. Natural surfactants present in the oil often result in stable oil-in-water emulsions being formed. In such oil/water emulsion, the water is present as small water droplets in a matrix of oil. Sometimes reverse emulsions are formed wherein the oil is present as small droplets in water as the continuous phase. To meet the pipeline specifications for bottoms, sediment and water (BS&W) generally requires removing the water, which was difficult and involves costly chemical and mechanical treatments. Generally (most) water is removed by a combination of gravity separation (sometimes mechanically aided) and by the addition of demulsifiers to break the emulsion. To remove the last traces of water, more severe measures are often required. In addition, certain emulsions, e.g. fireflood emulsions, are very difficult to break. Removal of the last amounts of water often is accomplished by flash evaporation, i.e., the oil is heated to above the boiling point of water. Finally after a clean, water-free oil has been obtained, the viscosity and density specifications still have to be met to allow transportation by pipeline. Again this is accomplished by mixing the oil with diluent.
The prior art has addressed the problem of how to transport such viscous material, while reducing the diluent requirements, by two general classes of treatment. The first class includes processes that do not affect the oil in any way and use water as a substitute for diluent. The second class includes processes that break up the constituent oil molecules and change its properties, thereby reducing both its viscosity and density. In both classes of treatments, the original emulsion water has to be separated first.
Processes in the first class reduce the viscosity by mixing the oil with water and surfactants to prepare an oil-in-water emulsion. This emulsion must be stable enough to withstand the diverse conditions it encounters in the pipeline system, e.g., the high shear stresses in the pumps, yet be easy to break at its destination.
Transportation of the oil using core annular flow is another proposed concept. Here an artificially created film of water surrounds the oil core concentrically. This reduces the viscosity and pressure drop almost to that which would be expected for water. These processes require that, where field emulsions are produced, these emulsions be broken first. Water, and in the case of emulsion transport, surfactants, are then added and mixed under controlled conditions to obtain a stable emulsion or core flow. In all cases where diluents or water are used, a significant part of the capacity of the pipeline is being taken up by a non-heavy oil component, significantly adding to the cost of the system. In the case of water, it might also create a disposal problem at the receiving end of the pipeline, and in the case of diluent, return lines will often be required to transport the diluent back to the field to be mixed again with heavy oil.
Processes in the second class alter the oil properties significantly and are generally of the carbon rejection or hydrogen addition type. Both procedures employ high temperatures (usually&gt;about 430.degree. C.) to crack the oil. In the carbon rejection processes, the oil is converted to lighter oils and coke, while in the hydrogen addition processes the formation of coke is prevented by the addition of high pressure hydrogen. In some coke rejection processes, the coke is burned or gasified to provide heat, or fuel that can be used elsewhere in the process. Both of these upgrading processes significantly increase the distillate yields, because of the thermal cracking of the heavy oil molecules that takes place, which results in significantly altered molecular weight structures and properties. However, because of the extensive cracking that takes place, these high conversion processes destroy the asphalt properties that many of the original heavy oils exhibit. This is a serious concern since asphalt is a high priced commodity.
All hydrogen addition processes require hydrogen to allow the process to proceed without coke formation. Some hydrogen addition processes are described in the prior art that use coke or effluent streams to generate carbon monoxide, which in turn is used to make hydrogen.
For example, U.S. Pat. No. 2,614,066, patented Oct. 14, 1952 by P. W. Cornell, provided a continuous method of hydro-desulfurization, in which the hydrogen utilized in the process was largely obtained from contaminant produced concomitant with the hydrodesulfurization process. The patented process comprised removing sulfur from petroleum hydrocarbons containing sulfurous material at an elevated temperature with a hydrogen-containing gas in the presence of a contact material having hydrogenating characteristics, cooling the effluent to obtain a first gas portion and a hydrocarbon liquid portion containing dissolved gases, separating the hydrocarbon liquid portion, and removing the dissolved gases from the hydrocarbon liquid to form a second gas portion. Substantial amounts of the hydrocarbon portion of this second separated gas portion were then converted into hydrogen through a reforming and shift reaction. The formed hydrogen was recycled for the hydrodesulfurization of the feed petroleum hydrocarbons.
U.S. Pat. No. 3,413,214, patented Nov. 26, 1968 by R. B. Galbreath, provided for the hydrogenation of liquid hydrocarbons which was carried out in the presence of hydrogen and a controlled amount of oxygen to hydrogenate a major portion of the liquid hydrocarbon feed and to oxidize a minor portion thereof, thereby producing a gaseous product containing carbon monoxide. The carbon monoxide content of the gaseous product was subsequently reacted with steam in a separate reactor to form additional hydrogen which was recycled to the hydrogenation zone.
U.S. Pat. No. 3,694,344, patented Sept. 26, 1972 by W. H. Monro, provided a combination process in which a hydrocarbonaceous charge stock was reacted with steam to produce an effluent containing hydrogen and carbon oxides. The relatively low pressure effluent was compressed to an intermediate pressure level, at which pressure the hydrogen concentration was increased through the removal of the oxides of carbon. The purified hydrogen stream was then compressed to a higher pressure level and was introduced into the hydroprocessing reaction zone.
U.S. Pat. No. 4,207,167, patented June 10, 1980 by R. W. Bradshaw, provided a process wherein a used hydrocarbon cracking catalyst having coke laydown thereon was regenerated under conditions to produce a gas rich in carbon monoxide which, together with steam, was subjected to a shift reaction to produce carbon dioxide and hydrogen. Oil cracked with such catalyst produced vapors which were fractionated to yield gases, cracked gasoline, a light-cycle oil, a heavy-cycle oil and bottoms, at least one of the light and heavy cycle oils is hydrocracked with the hydrogen earlier produced.
U.S. Pat. No. 4,569,753, patented Feb. 11, 1986 by L. E. Busch, et al, provided a combination process for upgrading residual oils and high boiling portions thereof comprising metal contaminants and high boiling Conradson carbon forming compounds. The process comprised a thermal visbreaking operation with fluidizable inert solids followed by a fluidized zeolite catalytic cracking operation processing demetallized products of the visbreaking operation. Solid particulate of each operation were regenerated under conditions to provide carbon monoxide rich flue gases relied upon to generate steam used in each of the fluidized solids conversion operation and downstream product separation arrangements. The wet gas product stream of each operation was separated in a common product recovery arrangement. The high boiling feed product of visbreaking comprising up to 100 ppm Ni+V metal contaminant was processed over a recycled crystalline zeolite cracking catalyst distributed in a sorbent matrix material.
Canadian Patent No. 1,195,639, issued Oct. 22, 1985 by H. S. Johnson, et al, provides a process for upgrading heavy viscous hydrocarbonaceous oil. The patented process involves contacting the oil with a carbon monoxide-containing gas and steam in a reaction zone at hydrocracking conditions, such hydrocracking conditions including a temperature of at least about 400.degree. C. and a pressure between substantially 5 MPa and 20 MPa, in the presence of a promoted iron catalyst, to yield a hydrocracked product. The required hydrogen to prevent coke formation was made from carbon monoxide and added water inside the upgrading reactor. No hydrogen or carbon dioxide was recovered.
Canadian Patent No. 1,124,195, issued to Khulbe et al, describes a hydrocracking process that operates from about 400.degree. to about 500.degree. C., where synthesis gas is used to supply the hydrogen for the cracking reactions. The synthesis gas was made in a separate reactor.
None of the patented processes described above are suitable for reducing both the viscosity and density of heavy oils without substantially breaking up the constituent molecules of the oil. In all the hydrocracking processes described above, the oil properties were changed significantly. Furthermore, in none of the described processes, was hydrogen and carbon dioxide recovered separately for use in alternative processes.